Transmitter control circuit



Aug. 5, 1947. L. DUBIN TRANSMITTER CONTROL CIRCUIT Filed April 2, 1945 atented Aug. 5, 1947 TRANSMITTER CoN'raoL CIRCUIT Lester Dubin, Brooklyn, N. Y., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware I q Application April 2, 1945, Serial No. 586,225

Claims.

This invention relates to automatic volume control circuits and more particularly to such control circuits applied to radio beacon transmitters of the omni-directional type.

Various forms of omni-directional radio beacons have been proposed in the past. One such form, as for instance disclosed by E. Labin-D. D. Grieg in their application for patent, Ser. No. 581,974, led March 10, 1945, contemplates a visual indicator beacon system which is applicable to various modulation methods wherein a directive radio beam is rotated and which is modulated in synchronism with its rotation about the transmitter position. The modulation 0f the beam is such that continuous indications may be had from an indicator at the receiver station in contrast to indications by azimuth segments as in some previous systems. In order that the bearings obtained with such a system remain independent of supply voltage changes or input or output signal amplitude level changes and so forth,rthe transmitter and receiver signals are provided in the form of components compared in ratio rather than absolute signal value. By this means the accuracy of the system maybe maintained independent of the operating parameters.

y It is an object of my invention to provide for omni-directional radio beacon system of the above-described type, apparatus suitable for transmitting Vsignals of given ratios for interpretation with respect'to directional information by a receiver.

It is a further object to provide a transmitter which will generate signals having ratios which will be maintained substantially constant.

It is still another object of the invention to provide a transmitter having great stability and constancy of operation and which automatically maintains such stability and constancy.

It is still another object to provide a circuit for accomplishing the above-defined objects.

In accordance with a feature of this invention, I provide an improved transmitter for use in a radio beacon of the type described in detail in the aforesaid application, briey described below. The transmitter is comprised of three separate oscillators for supplying three different frequencies.

The output circuitsfor two of the oscillators include the stator coils of a rotating variometer and the output circuit of the third oscillator is applied directly to a mixing circuit which also receives the output voltage of the other two oscillators. The two stator coils are arranged to forma 90 angle. The rotary coil is continuously 2 influenced by the respective elds of the stator coils in accordance with its rotative position relative thereto. The effect of this arrangement is such that the outputs oi the two rst signal sources or oscillators are modulated in accord ance with the sine and cosine functions respectively.

The third signal which does not go through the variometer consequently remains at a constant amplitude. These three signals are brought together in the mixer to produce a composite signal which is used as a modulating source for radio frequency transmissions. The modulated energy is transmitted in the form of a beam rotated in timed relation with the rotary coil of the variometer. As a consequence, the radiation pattern will contain the three modulation components having a unique mutual relationship or ratio for each azimuth position of the rotating beam.

In order to maintain the amplitude of the outputs of the three oscillators at a xed ratio, an automatic amplitude control is used, utilizing a rectifier circuit for each oscillator the rectiiiers all being referred to'a common reference, in this case a common source oi delay bias potential for the rectiers. Further improved stability of operation is obtained by the provision of considerable negative feedback in the oscillator and amplifier circuits related thereto.

These and Vother objects and features will be better understood from the detailed description made with reference to the accompanying drawn ing in which the single figure represents a diagram partly in schematic and partly in block form of the modulating signal generator circuits for the transmitter in a radio beacon system' of; the above-described type.

In the iigure the circuit is seen to coin-prise.l

threeoscillato-rs I, 2 Iand 3. The oscillators, as, shown in detail for oscillator I, are of the resistor-` capacity phase-shift type and are tuned to fre-` quencies F1, F2 and F3, respectively. They each include an oscillator tube d which receives its, plate energy from a B+ supply 5 over a plate load resistor S. The supply 5 also provides a load potential for a screen grid 'I over a screen resistor 8, the latter being bypassed to ground by a condenser 9. The oscillator tube 4 is provided with a negative feedback in the form of an. unb-ypassed cathode resistor Il) and with a frequency deter-v mining circuit consisting of a three-mesh seriescondenser shunt-resistor network, which includes condensers II, I2, I3 and resistor circuits I4, I5, and I6, of which the circuits I4 and I5 are tied 3 to a common ground at l1. These resistor circuits I4, l5 and I6 are subject to a ganged adjustment as shown at I8- in order to permit a suitable phase correction. A positive feedback is established over the frequency determining R.C'. mesh circuit connected to grid I9 of the oscillator tube 4. The output of the oscillator circuit is applied over a coupling condenser 2ilto an amplifier 2 I; in the rst channeland amplifiers 22 and'r2'3 in the other respective oscillator channels. These amplifiers each comprise an amplifier tube 24 which receives its control energy on a grid 25 over the coupling condenser 20. The grid 25 and a cathode 26 are biased by means of resistors 21 and respectively which are connected together to-a negative. feed# back resistance 29. The amplifier tube 24 is'pro-Y vided with a plate 30 and a screen 3l, both of` which are supplied with potential from the source 5, the grid over a screen grid resistor 32 and the plate over the primary Winding 33 of an output step-up transformer 34. Transformer 3,4V issplitn to provide two windings. A normal outputcircuit of a rotary coil 40 which` isl afunction of its :rotary position with respect to the two statorcoils Vis also applied to one of the mixerstages at 38; The other secondary Winding 4| of the output 'transformer 34, which is tuned by means-of a condenser 42 connected thereacross tov improve the Waveform and to increase a voltage output "thereof, feeds an automatic volume control ciricuit 43, in the channel of the first oscillator, and :similar volume control; circuits 44 andA 45` for the other two oscillators. To obtain the automatic voltage control the voltage of the transformer secondary 4l is applied toa cathode 45 ofa diode rectifier 4l. volume control circuits 43, 44, and 45 are furf. nished with a common delay bias` from the source 5 applied to the respective cathoclesl by way ofA The output.

the windings of the secondary 4|; voltage of the diode rectifier 41, asdeveloped across its load resistor 48 Which is bly-passed by a condenser 49,. is fed back over a conductor 5 53 and analogous conductors 5Iv and 52V in theIv case.V

of the othertwo oscillators as a control bias volt,- age to the control grid i9- of the oscillator tube 4 by way of the resistor circuit i6.

In operation, the oscillators I, 2, anda supplyl signal frequencies preferably in the audio range, designated as F1, F2, and F3. These frequencies are each determined by the respective R..C.

meshes and the plate and load resistors Vof the respective oscillators. Corrective adjustments in the frequency may be made by means of theV gangedadjustors I8 in each of the mesh networks. The oscillators output is amplified inthe ampli? The diodes of the` threeautomatic ner circuits 2l, 22, and 23, the outputs off which in part will supply voltages to the two variometer stator coils 31 and 3.9 and to the mixing circuit amplitude o-f the threeoscillato-rs must always be maintained in. a fixed ratio since otherwise the ultimate azimuth in formation will'lbein error.

In order to keep the three oscillator voltages in a fixed ratio, a common delay bias is applied to al1 of the three diode rectiers. This common bias thus acts as a reference for the three oscillators. IThe larger the signal voltage applied to the diode in comparison With the D.C. control voltage developed thereby, the more effective will be the automatic amplitude control. Since the modulating output voltage to thestator coils is taken from a low impedance winding on the output transformer 34 distortion should be held to a minimum. Toachieve this, the full output of the oscillator is applied to the amplifier tube grid and a large negative feedback is used. The amplifier tube shouldbe such so as to have enough gain tol utilize all the feedback possible. A common voltage supply is used to provide the operating potentials for the oscillator, amplifier and the rectier tubes. Should any of the amplifiers' have a reduced output due to any cause whatsoever such las variation of supply voltage,rchangesin the tube characteristics or variations inthe indi-Vr vidual oscillator outputs themselves then theau-l tomatic volume control of the separate circuits Will serve to bring these back to the valuedetermined bythe commonV delay bias. The reference, voltage, itself, may lbe subject to regu-lation to improve general operation stability.

Since the vario-meter, as already disclosedin the above-mentioned copending applications,

comprises two stator coils physically at an angleY of 9G". to one another and aurotary coil, each of` the stator coils. induces a voltage in the rotary c oil which-varies sinusoidally in amplitude in the rotary coil. Due to the relativev positions of the two stator coils, the amplitude variations ofthe two voltages induced in therotary coil are 90." out of phase, that is, one is a sine and the other a cosiner function ofthe rotary angle. The'outputv of the three oscillator circuits, therefore, will consist. of two varying amplitude voltagesV each consisting of a` fixed amplitude component supe.

plied by a stator coil and a varying amplitude component supplied by the rotary coil, and a fixed amplitude voltage connected directlytothemix-` ing network 38.- f'

In view of they necessity as shown above, for thepro-per operation` of the beacon system for the ratio ofthe signals of the. respectiveoscillators to be maintained substantially constant, the im-v portance of the automatic volume control having a common reference and of the considerableynegaf.

tive feedback for imp-roving the stability of operation of the system will be appreciated.

While Ihave described my invention particu-Y larly in connection with a rotary radio beacon, it shall be understood that this is` only one-fuse thereof. My invention may be used wheneverlit is requiredy that the ratio of energies from twoor more oscillators be maintained substantially con# stant. c

It will Ibe understood that the particular enibodiment as given above is presented merely by;V Way of illustration and should not be considered as a limitation of my invention as set forth ,iny

the objects thereof.

I claim:

1. A radio circuit for generating a composite.-

signal consisting vof a plurality of signals hav-ing constant mutual ratios, comprising a pluralitylofoscillators, one eavchfor generating a signal at a given frequency, signal amplifying meansA for each oscillator, a load output circuit-for eachof said amplifying means, a control'output coupled to each of said amplifyingmeans forY deriving a corrective biasing Voltage therefrom, means for applying said biasing voltage to the respective oscillators, to compensate for variation in amplitude of the output energy thereof, and means for applying a delaying bias common to all of said control circuits, whereby a common reference is obtained for said oscillators.

2. A circuit in accordance with claim 1, Vwherein said control output circuit comprises a. rectifying diode.

3. A circuit in accordance with claim 1, further including means for producing negative feedback for each of said oscillators and said amplifying means.

4. A circuit in accordance with claim 1, wherein each of said amplifying means includes a stepup transformer having a secondary portion for energizing said load output circuit and another secondary portion to energize said control output circuit.

5. A circuit in accordance with claim 1, wherein said plurality of oscillators are three in number and the load output circuits of two of said oscillators include the two stator coils of a Variometer comprised of two stator and one rotary coil, further including a mixing circuit for combining the outputs of said ampliers and of the rotor of said variometer.

LESTER DUBIN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

